Indian scientist among those who made building blocks of quantum computer

A young Indian scientist and his colleagues have come out with what may be the building block of a practical quantum computer, opening a new door to realise the long-awaited number cruncher that may be more commonly available than the few machines that now exist in secluded laboratories around the world.

What the trio of Michael Kues, Hatam Mahmudlu and Raktim Haldar and their colleagues in Germany and Netherlands have done is to come out with an ultra-small, robust, stable and scalable chip to produce photonic qubits (quantum equivalent of bits) using a “novel and tricky architecture” for designing.

The photonic chip they created can operate in room temperature and does not need a super-cold environment close to Absolute Zero (minus 273 degrees Celsius) that most of the current crop of quantum computers – including the ones made by IBM – requires. Google’s Sycamore quantum processor also needs a similar cryogenic condition.

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“We developed the world's first fully-integrated on-chip quantum light source that works at room temperature. The chip can be commercially-viable bringing the required stability and scalability for a quantum computer,” Halder, who graduated from Indian Institute of Technology, Kharagpur and currently researching in Germany told DH.

The chip whose size is less than a one euro coin contains a fully operating laser and noise filter. “Such tiny and compact qubit sources can be used as a building block of any quantum processors, or can reduce the payload of quantum satellites,” he added.

For decades, scientists have been exploring different avenues to come up with quantum computers with little success. Last month India also announced a Rs 6,000 crore national mission to develop quantum computers, communication and sensors.

There are multiple routes to develop quantum computers, but the commonest approach is using a super-conducting platform as qubits can be controlled easily in such a platform.

However, on the downside, creating a super-conducting state requires huge investment to create a cryogenic environment. Tech giants like IBM and Google followed such an approach.

A second route using photons (light particles) is also being probed as photonics doesn’t require cryogenic temperatures and hence is an advantage over systems that need stringent cooling.

“The photonic qubit architectures are quite different and in principle can lend itself to more scalability, provided technical issues are resolved,” explained an Indian quantum scientist not associated with Halder’s project.

Photonic quantum computers need special photonic chips, which are not new. But the problem with the current generation of such chips is that they needed to be connected to bulky lasers as big as a table and big filters to work.

The entire process is cumbersome, requires a laboratory and an expert hand to operate the laser. In addition such chips are also unstable.

Halder and his team at the Institute of Photonics at Leibniz University have overcome this fundamental challenge. They have been able to cram an entire laser and a filter onto a single chip, which have not been possible before.

Moreover, due to an efficient filter, the chip is capable of delivering qubits without errors by efficiently removing noise, which is essential for building quantum computers. In addition, it is very small, light, easy to carry and above all doesn't require any special skills to operate.

"Our breakthrough allowed us to shrink the laser size by a factor of more than 1000 allowing reproducibility, stability over a longer time, scaling, and potentially mass-production. All these characteristics are required for real-world applications such as quantum processors,” said Michael Kues who heads the Institute of Photonics.

The study has recently been published in Nature Photonics.